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Abstract

The whiteness of fluorescent white materials is in part due to the absorption of ultraviolet (UV) light and subsequent emission of visible blue light. The UV content of light sources in viewing booths and in spectrophotometers can thus significantly affect the perceived whiteness (PW) and measured sum of reflected and emitted light of fluorescent materials. The effect of UV content on the spectral radiance factor of fluorescent white materials containing different amounts of a fluorescent brightening agent and the subsequent assessment of their PW were evaluated. The UV content of sources in two calibrated viewing booths that simulated D65 and D75 illuminants, separately, was changed by selectively blocking UV emission of the source by approximately 0%, 25%, 50%, 75%, and 100%. The radiance spectra of a series of white fabrics were also obtained using a reflectance spectrophotometer at 0%, 25%, 50%, 75%, and 100% UV transmittance. The CIE and Uchida whiteness indices (WIs) were calculated for white samples and compared to perceptual results under varying illumination and UV conditions. Results indicate relatively modest agreement between perceptual assessments of fluorescent samples and whiteness metrics examined. Results also show that when the UV content of sources used in the viewing booths is adjusted to be similar to that used in measurements, improved correlations between perceptual and calculated results are obtained. The CIE WI was found to outperform the Uchida index under both sources.

References

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Table 2.

Quality of D75 Daylight Simulator in SpectraLight-III Booth

Table 3.

Mean Inter- and Intrasubject Variability (Coefficient of Variation) Expressed in PW Units in the Determination of PW

UV %

Mean Intrasubject Variability

Mean Intersubject Variability

0

3.83

3.94

25

1.31

1.35

50

2.13

2.10

75

3.09

3.13

100

0.88

0.90

Table 4.

Effect of Variations in UV on Measured and Perceived CIE WI of Nonbrightened and (0–2.5%) FBA-Treated Samplesa

Instrumental Whiteness Values

Perceived Whiteness Values

D65+%UV

0%

0.025%

0.25%

2.50%

TUVCS

0%

0.025%

0.25%

2.50%

TUVCS

0

71.0

80.6

81.8

70.2

58.1

81.9

102.4

108.7

96.1

93.1

25

70.9

87.1

90.6

79.1

65.8

82.2

106.7

111.4

98.0

96.7

50

71.9

107.3

121.3

109.9

92.0

80.9

109.0

113.2

96.9

105.3

75

71.6

123.8

143.2

132.2

111.4

81.1

105.1

113.2

104.3

107.9

100

72.3

128.0

146.9

137.1

116.9

81.3

105.1

109.0

104.2

105.6

D75+%UV

0

70.3

79.9

80.8

68.2

56.7

81.7

107.2

113.3

86.7

93.3

25

70.2

86.7

89.9

77.4

64.7

83.3

104.7

112.9

97.0

102.9

50

71.2

107.5

121.5

109.1

91.8

81.2

107.7

116.4

106.0

111.0

75

71.0

124.5

143.8

131.8

111.4

81.2

108.6

118.1

106.0

111.0

100

71.7

128.7

147.5

136.9

117.4

81.8

107.4

117.8

106.1

113.7

a Correlation coefficients are reported for each UV level shown in the column and the corresponding PW values under the same relative UV amounts used for perceptual assessments in viewing booths (i.e., 25% versus 25%).

Table 5.

Effect of UV Content on PW of Nonbrightened and (0–2.5%) FBA-Treated Samples under D65 and D75 Illuminationsa

D65 Illumination

D75 Illumination

UV Level

All Samples

Fluorescent

All at Cal. UV

All Samples

Fluorescent

All at Cal. UV

0% UV

0.60

0.91

0.92

0.65

0.78

0.71

25% UV

0.79

0.90

0.91

0.61

0.58

0.90

50% UV

0.83

0.35

0.87

0.87

0.41

0.95

75% UV

0.93

0.48

0.95

0.92

0.48

0.95

100% UV

0.95

0.57

0.95

0.91

0.26

0.92

a Correlation coefficients are reported under a given measured UV level for PW and instrumental results under the same UV% used (i.e., 25% Versus 25%). The “Fluorescent” column does not include the nonfluorescent sample in the calculation of correlations. For the “All at Cal. UV” results, the correlation is between each UV level against measurements at the calibrated UV level (78.7%) according to the AATCC procedure.

Table 6.

Some Useful Radiometric Units and Terms

Name

Units

Illuminated Object

Irradiance=radiant incidence

W·m−2

Spectral irradiance

W·m−2·nm−1

Light source

Radiant exitance

W·m−2

Radiant intensity

W·sr−1

Spectral radiant intensity

W·sr−1·nm−1

Radiance

W·m−2·sr−1

Spectral radiance

W·m−2·sr−1·nm−1

Tables (6)

Table 1.

Quality of D65 Daylight Simulator in SpectraLight-III Booth

Booth UV Setting

Mv

Mu̲

CIE Quality Grade

0%

0.38

3.15

BE

25%

0.39

3.05

BE

50%

0.40

2.14

BE

75%

0.41

1.45

BD

100%

0.46

0.36

BB

Table 2.

Quality of D75 Daylight Simulator in SpectraLight-III Booth

Booth UV Setting

Mv

Mu̲

CIE Quality Grade

0%

0.97

2.97

CE

25%

0.97

2.26

CE

50%

0.98

1.71

CD

75%

0.98

1.14

CD

100%

0.98

0.34

CB

Table 3.

Mean Inter- and Intrasubject Variability (Coefficient of Variation) Expressed in PW Units in the Determination of PW

UV %

Mean Intrasubject Variability

Mean Intersubject Variability

0

3.83

3.94

25

1.31

1.35

50

2.13

2.10

75

3.09

3.13

100

0.88

0.90

Table 4.

Effect of Variations in UV on Measured and Perceived CIE WI of Nonbrightened and (0–2.5%) FBA-Treated Samplesa

Instrumental Whiteness Values

Perceived Whiteness Values

D65+%UV

0%

0.025%

0.25%

2.50%

TUVCS

0%

0.025%

0.25%

2.50%

TUVCS

0

71.0

80.6

81.8

70.2

58.1

81.9

102.4

108.7

96.1

93.1

25

70.9

87.1

90.6

79.1

65.8

82.2

106.7

111.4

98.0

96.7

50

71.9

107.3

121.3

109.9

92.0

80.9

109.0

113.2

96.9

105.3

75

71.6

123.8

143.2

132.2

111.4

81.1

105.1

113.2

104.3

107.9

100

72.3

128.0

146.9

137.1

116.9

81.3

105.1

109.0

104.2

105.6

D75+%UV

0

70.3

79.9

80.8

68.2

56.7

81.7

107.2

113.3

86.7

93.3

25

70.2

86.7

89.9

77.4

64.7

83.3

104.7

112.9

97.0

102.9

50

71.2

107.5

121.5

109.1

91.8

81.2

107.7

116.4

106.0

111.0

75

71.0

124.5

143.8

131.8

111.4

81.2

108.6

118.1

106.0

111.0

100

71.7

128.7

147.5

136.9

117.4

81.8

107.4

117.8

106.1

113.7

a Correlation coefficients are reported for each UV level shown in the column and the corresponding PW values under the same relative UV amounts used for perceptual assessments in viewing booths (i.e., 25% versus 25%).

Table 5.

Effect of UV Content on PW of Nonbrightened and (0–2.5%) FBA-Treated Samples under D65 and D75 Illuminationsa

D65 Illumination

D75 Illumination

UV Level

All Samples

Fluorescent

All at Cal. UV

All Samples

Fluorescent

All at Cal. UV

0% UV

0.60

0.91

0.92

0.65

0.78

0.71

25% UV

0.79

0.90

0.91

0.61

0.58

0.90

50% UV

0.83

0.35

0.87

0.87

0.41

0.95

75% UV

0.93

0.48

0.95

0.92

0.48

0.95

100% UV

0.95

0.57

0.95

0.91

0.26

0.92

a Correlation coefficients are reported under a given measured UV level for PW and instrumental results under the same UV% used (i.e., 25% Versus 25%). The “Fluorescent” column does not include the nonfluorescent sample in the calculation of correlations. For the “All at Cal. UV” results, the correlation is between each UV level against measurements at the calibrated UV level (78.7%) according to the AATCC procedure.